Research On Ultra-precision Processing Of Scintillator And High-reflectivity/High-Transmittance Films

Positron emission tomography is the most sensitive medical imaging instrument for data display and quantitative analysis of human normal metabolism and pathological changes.It is used for early diagnosis and staging of major diseases such as cancer,heart disease,and nervous system diseases.The scintillator-based high-energy ray detector module is the key component of PET equipment,and improving the energy resolution and time resolution of the detector is important for promoting the performance of PET system.The processing quality of scintillator surface and the reflector wrapped on the outer scintillator surface affect the light output of the crystal end,which thereby affects the detector energy resolution.The light transmittance of scintillator end surface,the surface coupled to the photoelectric sensor,affects the detector's initial photoelectron rate,thereby affecting the time resolution of the detector.In order to improve the energy resolution and time resolution of the detector,this paper proposes three main research contents:?1?Ultra-precision processing technology of cerium doped lutetium-yttrium oxyorthosilicate scintillator?LYSO?;?2?Design and preparation of high-reflectivity film based on the emission spectrum of LYSO scintillator;?3?Design of high-transmittance film based on the emission spectrum of LYSO scintillator.In the study,the LYSO scintillator was precisely processed by plane grinding and polishing method.The surface defects of the scintillator were firstly removed by alumina abrasives with different size,and then the scintillator was precisely polished with cerium oxide polishing solution.The surface roughness is lower than 1nm after processing,which means the goal of ultra-precision processing of LYSO scintillator is achieved.Based on the principle of multilayer dielectric reflective film,we designed a high-reflectivity film stack?HR?with a total layer number of 48 layers which match the entire emission spectrum of LYSO scintillator.The film stack is consisted of three ?/4 wavelengths basic reflective film,including TiO₂/SiO₂/HfO₂ dielectric material.Based on the design of reflective film stack,the reflective film was prepared by electron beam evaporation method.The tested reflectivity is highly consistent with the designed results.Based on the principle of multilayer dielectric antireflective film,a 7-layer anti-reflection coating which covers the entire emission spectrum of LYSO scintillator was designed.The coating was composed of MgF₂/TiO₂/HfO₂.Coating the scintillator end surface with antireflection film and taking optical glue as the coupling medium between the scintillator end surface and photoelectric sensor are conducive to increase the light transmittance comprehensively.